1. Field of the Invention
The present invention relates to a method of correcting a speed of an encoder and an apparatus therefore. More particularly, the present invention relates to a method of correcting a speed of an encoder by selecting an intermediate speed value and an apparatus therefor.
2. Description of the Related Art
An optical encoder method is commonly used for detecting a driving speed of a driving shaft such as a motor or a driving speed of the driving shaft of a driven system driven by the motor.
According to the optical encoder method, a disk along whose circumference a plurality of slits are arranged at regular intervals is fixed to the driving shaft of the motor, and an encoder sensor unit including a light emitting portion and a light receiving portion detects the above-described slits.
A controlling unit calculates the driving speed of the motor by an electrical signal output from the encoder sensor unit.
A method of calculating the driving speed of the motor will now be described. The driving speed is calculated through an H level section and an L level section of the electrical signal output from the encoder sensor unit. The position of the encoder sensor unit is set such that a length of the H level section is equal to a length of the L level section.
However, one difficulty experienced when the driving speed of the motor is detected by such a method, is that in order to make the length of the H level section of the electrical signal output from the encoder sensor unit equal to the length of the L level section of the electrical signal output from the encoder sensor unit, it is required to precisely install the encoder sensor unit, which may require significant effort.
When the encoder sensor unit is not precisely installed, errors are generated in detecting the driving speed of the motor by the length of the H level section of the electrical signal output from the encoder sensor and the length of the L level section of the electrical signal output from the encoder sensor. In order to solve such a problem, according to a conventional method of correcting the driving speed of the encoder, the sum of the length of the H level section and the length of the L level section is set to one period to measure a corresponding speed.
However, according to the conventional art, although the slits are arranged at regular intervals to total 360 degrees in manufacturing a wheel encoder, the distance between the first slit and the last slit may not be perfectly uniform. Thus, the speed detected in the corresponding period includes an error value due to a deviation in the distance between the slits.